One of the things climate change or global warming deniers like to do is to use unadjusted temperature data to try and ‘prove’ that temperatures aren’t increasing and that the 1930s were just as warm as now. I posted the following to a Facebook page (Australian politician Craig Kelly’s) in response to a few denier comments about homogenised data just being part of the climate change ‘fraud’.

No use looking at raw data. It has to be adjusted or homogenised data. This is done by weather bureaus all around the world to take out non-climatic changes such as shifting weather stations and changing measuring methods. Three main things have to be adjusted for.

Over the decades, weather stations have typically moved from post offices in the centre of town, where it is warmer especially at night (urban heat island effect) to airports on the outskirts of town in green open fields where it’s cooler. This is why raw temperatures in the 1930s are often about as high as now (the move to airports was generally from about the 1940s onwards). This non-climatic change to temperatures has to be taken out to get a true picture of how temperatures have changed.

It can go the other way too; for example, town-based weather stations that haven’t moved might now be surrounded by more concrete and steel than decades past.

Also, temperature measuring methods have changed and this can have an effect. In the 19th century, instruments were typically attached to walls of buildings and protected from the sun by metal screens but this had the effect of pushing up temperatures. Instruments were then put in gardens away from buildings but infrared radiation from the ground could push up temps on calm sunny days. High-tech automatic weather stations that counter these sort of problems are now common.

Once all the adjustments are made, we can get a far more accurate picture of how temperatures have actually changed rather than changes influenced by the shifting of weather stations or different measuring methods.

In Australia, new senator and climate denier Malcolm Roberts appeared on television on the ABC’s Q&A program last Monday, 15 August 2016. I posted the following comment on his Facebook page but it got deleted and I got tossed off (haha). I guess the truth sometimes hurts …

After watching Q&A, I think I’m figuring out why Malcolm Roberts keeps saying there is no empirical evidence for warming or AGW [anthropogenic global warming] despite abundant evidence. He just doesn’t believe in any of the data that shows warming. Brian Cox [physicist and television presenter] showed a graph of NASA data that clearly shows significant warming since the 19th century. Roberts said not true as the data is corrupted and manipulated, by NASA. His reason for this: a well known denier, Steve Goddard showed that the 1930s were allegedly warmer than the current decade and that 1930s recordings were reduced and latest decade inflated, and that BOM [Australia’s Bureau of Meteorology] did the same.

Seems that much or most of the problem was Goddard’s failure to understand that raw data is adjusted to give a truer picture, including estimates of missing data. Statistics of all sorts are adjusted for seasonal and other impacts. It means the data gives a more accurate representation of what is actually happening. All official statistical agencies around the world do it for all sorts of collections. Temperature data are also adjusted. Weather recording stations move and this can have a big effect on temperature; moves from a post office to an airfield have been common. Adjustments are also made due to changes in measuring instruments and their accuracy over the years. Another reason is that a weather station may become more closed in, such as by additional nearby buildings, which can affect temperatures. These things are taken into account by all weather bureaus around the world.

Hunt [Greg Hunt, ex-environment minister, now industry minister] wasn’t buying Roberts’ argument for no warming either. He pointed out that weather bureaus, scientific organisations and leading universities all come to the same conclusion: global warming is real. Serna [Lily Serna, mathematician and television presenter] couldn’t believe we were still having this conversation, that there was overwhelming consensus from scientists who are the experts in their field, and that we should be getting on with mitigation and adaptation. Roberts said consensus isn’t science and that he still needs empirical evidence. Cox tried to explain the scientific process to him, including measuring temperature and CO2 and making predictions. Roberts said the numbers have been hopelessly wrong.

My conclusion was that Roberts doesn’t understand scientific or statistical processes and just looks for any odd bit of data that supports his case for no warming and especially no AGW. I’ve looked at statistical adjustment above. On models, we can get an idea of what might happen, but it’s impossible to know exactly how hot it will be or how far sea levels will rise in however many years’ time, just as it is impossible to know what the economic growth rate will be: there are just so many variables. On consensus, the following is probably the best empirical evidence there is for warming and AGW, i.e. looking at the metadata:

– In 2013, John Cook et al looked at about 12,000 academic papers on climate change / global warming, covering all sorts of issues. They found that 66.4% of abstracts had no position on AGW, 32.6% supported it, 0.7% didn’t and 0.3% were uncertain. Thus about 97% of papers with a view on AGW supported it. According to Roberts on Q&A, the figure for support was 0.3%, which is strange given that most scientific organisations have a statement supporting AGW [and most governments accept it too].

– In 2004, Naomi Oreskes analysed 928 papers published between 1993 and 2003. About 75% went with the consensus view of AGW, 25% were about methodology and paleoclimatology, and 0% opposed the consensus view.

– In 2007, Harris Interactive took a random sample of 489 members of the AMS and two other relevant bodies and found that 97% agreed with global warming, with 84% saying it was AGW and 5% said there wasn’t AGW.

– Bray and von Storch found that 40% of climate scientists agreed with AGW in 1996, 53% in 2003 and 84% in 2008.

– Doran and Zimmerman in 2008 found 97% agreed with AGW.

– A National Academy of Sciences study in 2010 put it at 97-98%.

– James Powell in 2013 found 24 of 13,950 articles disagreeing with AGW. In 2014, Powell found 1 author out of 9136 rejecting AGW.

And of course all national and international scientific organisations believe there is warming and most of it is due to our activities except a handful of geology groups that are still sitting on the fence.

Some conspiracy, like thousands of scientists around the world study in areas relevant to climate science and undertake careers in science to be involved in a scam; ditto all scientific organisations; and governments of all major countries. Yeah, and the world is flat too.